Generally, this invention relates to truck control systems for railway cars and more particularly this invention relates to constant contact side bearings for railway car trucks.
Two of the major truck control problems are truck hunting and lateral car body roll or rock and roll.
Truck hunting results from unrestrained fore and aft swiveling and can be set up by the normal rail following motion of the trucks on a car operating at light load and high speed as it follows the rails through a curve. Uncontrolled truck hunting causes flange wear and contributes to "nosing" resulting in overall wear of the truck parts and ultimately leading to derailment should the wheel flange climb the rail.
Lateral car body roll occurs in the case of heavily loaded cars operating on uneven road beds. Lateral car body roll usually results in impact contact between the bolster gibs the truck side frame. The lateral role condition is believed to occur in the following sequence:
1ST., INITIAL LATERAL CAR MOVEMENT RESULTING FROM TYPICAL CENTER PLATE CLEARANCES;
2ND., FOLLOWED BY A COMPRESSION PIVOTING MOVEMENT WHERE THE TRUCK SPRINGS GO SOLID AT A TIP ANGLE OF 18.degree.;
3RD., FOLLOWED BY CLOSING THE NOMINAL CLEARANCE BETWEEN THE BODY AND BOLSTER SIDE BEARINGS;
4TH., AND FINALLY A LUNGING MOTION AS THE CAR BODY CONTINUES ITS ROLL ANGLE UNTIL THE BOLSTER GIBS CONTACT THE SIDE FRAME COLUMNS -- THIS HIGH IMPACT CONTACT IS THE MAIN TRUCK DAMAGE PROBLEM ASSOCIATED WITH LATERAL CAR BODY ROLL.
Many designs of constant contact type side bearings have previously been employed but none of these has satisfactorily handled both truck hunting and lateral car body roll. If the side bearing is unduly stiff, it will eliminate truck hunting but at the expense of impairing the ability of the truck to swivel as required as it enters a curve and for returning to normal as it exits from a curve. If the side bearings is too soft, in order to accomodate free truck swiveling as required for following a curve, it will not adequately control truck hunting and it will be largely ineffective in controlling lateral car body roll.